Acclimatisation on Aconcagua The main problem faced by trekkers is trying to climb too quickly. From a medical perspective, we are trekking in very high altitude (up to 5,500m) and in extreme altitude (up to 6,962m). At sea level, the standard barometric pressure is 101 kPa. At 6,962m on the summit of Aconcagua, the standard barometric pressure is 43 kPa. This lower oxygen pressure means that there are fewer oxygen molecules in the same volume of air - there is only 43% of the oxygen available compared to sea level. Your body reacts to this lower oxygen level in a variety of ways - for example, your respiration (breathing) rate increases, and your body starts to generate more red blood cells. The respiration increase begins immediately, but the production of extra red blood cells takes longer. We are following a classic climb high / sleep low itinerary profile with a number of rest days and the ascent of a nearby 5,000m peak to ensure that we give our bodies more time to acclimatise to the lower oxygen levels before summit day. We recommend that you discuss with your GP the option of using Diamox (acetazolamide) to help prevent Acute Mountain Sickness (AMS).